A wind turbine system may comprise a wind turbine tower, a nacelle mounted at a top of the tower, wherein the nacelle houses a generator. One or more rotor blades may be connected to a rotation shaft of the generator. The rotation shaft may comprise one or more (permanent) magnets which are distributed along a circumferential direction (perpendicular to the rotation shaft). The generator may further include a stator coil arrangement comprising plural stator coils which are arranged such that a voltage and a current is induced upon rotation of the at least one magnet connected to the rotation shaft. Since a rotational speed of the rotor may depend on a wind speed, on an orientation of the nacelle relative to a wind direction, on a blade pitch angle of the one or more rotor blades and on other factors, the induced current and voltage (or electric energy) may oscillate with a variable frequency. For supplying the electric energy provided by the generator to an utility grid which supplies electric energy to one or more consumers, the electric energy (or voltage and/or current) generated by the generator needs to be transformed to a fixed frequency voltage and current (or energy flow), wherein the fixed frequency may correspond to a predetermined utility grid frequency, such as 50 Hz or 60 Hz.
For this purpose, the stator coil arrangement may be connected to a converter which may be adapted to convert the variable frequency input voltage provided by the generator to a fixed frequency output voltage or current (or energy flow). In particular, the converter may be considered as a particular representation of a power electronic device, in particular including one or more power transistors, such as isolated gate bipolar transistors (IGBT). A conducting state of the plural power transistors included in the converter may be controlled by one or more control circuits which switch the power transistors at a high frequency.
Thereby, there may be a risk that the converter fails. In case of such a failure the whole generator has to be shut down immediately until the faulty converter is fixed or replaced. In the meantime no electric energy can be produced by the wind turbine, reducing the efficiency of the wind turbine.